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From: jimp@cognos.uucp (Jim Patterson)
Newsgroups: comp.os.vms
Subject: Re: Need faster VMS spawn
Message-ID: <633@cognos.UUCP>
Date: Thu, 30-Apr-87 16:19:58 EDT
Article-I.D.: cognos.633
Posted: Thu Apr 30 16:19:58 1987
Date-Received: Sat, 2-May-87 08:25:00 EDT
References: <8704230311.AA00968@uvabick.UUCP>
Reply-To: jimp@cognos.UUCP (Jim Patterson)
Distribution: world
Organization: Cognos Incorporated, Ottawa, Canada
Lines: 31

I'm replying to your posting just to correct some apparent misunderstandings
about a few of the VMS services.

>In VMS, ...
>They have LIB$SPAWN, which is a higher-level interface to SYS$CREPRC, 

There are some significant differences between LIB$SPAWN and SYS$CREPRC
besides the interface itself.  Primarily, LIB$SPAWN is intended to create
a copy of your DCL session (or other command-interpreter).  This involves
copying over process logicals, DCL symbols and other tid-bits of information.
SYS$CREPRC does none of this, but simply runs another program/process.
(That's why it runs so much faster).  However, because it doesn't copy
over this environment, it also doesn't provide the same user environment
that was available to the command interpretor user.
Before LIB$SPAWN was provided (in VMS 3.0), it was extremely difficult in
VMS to implement the equivalent of the unix system() call.


>You will have to look at the System Services manual to find out what it's
>called, but I know that there is also a "exec"-like routine that overlays all
>or part of your address space with a new program image.  

You won't find this in the system services manual.  The routine you're
referring to is the image activator, and it's used by DCL to merge a user
program or image into the process address space as part of a RUN command.
It's not intended to be called by user programs directly.
However, you're right that it is implemented as a system service. 

-- 
Jim Patterson
Cognos Inc.